Reversible structural transformations related to the changes in environmental conditions are attracting considerable attention due to their potential use in functional devices, such as molecular sensors. Different stimuli (e.g., humidity, vapour exposure, temperature) can trigger a phase transformation in the solid state, resulting in a small displacement of atoms in the crystal lattice, which leads to a change in material properties. Herein we report on the synthesis and structural, as well as electrical characterization of metal-organic complex salt containing a bicyclic amine cation (CH3–DABCO)+ (1-methyl-4-aza-1-azoniabicyclo[2.2.2]octan-1-ium) and a bis(oxalato)chromium(III) anion [Cr(bpy)(C2O4)2]– (bpy = 2,2'-bipyridine). Following the principles of green chemistry and due to the low solubility of the chromium(III) precursor, the complex salts were prepared by mechanochemical synthesis. Single crystals were subsequently grown from the methanolacetonitrile solution of the prepared complex salt as methanol solvate (CH3–DABCO)[Cr(bpy)(C2O4)2]·MeOH (1MeOH) The interesting optical phenomenon of pleochroism was observed in these crystals, where they change color from dark orange to purplish red if rotated under the plane-polarized light. When exposed to the air with low relative humidity, these crystals transform to the dry form (CH3–DABCO)[Cr(bpy)(C2O4)2] (1). In a humid atmosphere with RH > 90%, the dry form is converted to the pentahydrate form (CH3–DABCO)[Cr(bpy)(C2O4)2]·5H2O (1H2O). The structural and electrical properties along with the dynamics of the transformation between the different forms were investigated by a combination of single crystal and powder X-ray diffraction, thermal analysis, infrared spectroscopy and chronoamperometric measurements.